In that caliber with traditional bullets, 95 or 100 grains seems to be the usual deal for deer. Consequently, dropping to 85 with a solid copper bullet tends toward light for caliber - on deer. I have used a 6mm to take many caribou; never shot and elk - with anything. Caribou are neither as large, on average, nor anywhere near as tough to bring down from what I read and hear.
I've also killed a fair number of caribou with the 7mm-08, a more resounding stopper than the 6 with any bullet typically. While the 140 XFB would sail through the animals from any angle at quite a distance, I could not count on that from the 85 X in the 6.
At the very least I'd bump up the weight on that bullet. If that means going to the fatter caliber, then do it. Otherwise, using your proposed combination, while possible, seems really limiting. But, perhaps your season is too long and the opportunities too many
? (I'm curious how the 280 is weightier than the 6 though. Maybe you need to swap scopes - or even buy another rifle.
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